Tall tail

[gyroo]

Hi Mad Muz,I appreciate your clarification. When I manage to clear my current workload I will be calling for G0023"s docs, and by saying so openly I reckon that by the time I do call for them that they"ll probably be competely in order

[MadMuz]

No worries Mark, I think many of us would like to know the figures and to have a list on hand to see which are better or which are worse..... I wonder if any factory machine owners have actually done an accurate test and would like to put some of us out of our misery and let us know? Even if they could PM you and you can pass it on as with no names mentioned, just the type? I for one would find it fascinating.... and to see if what it looks like to me is what it is, or if my eyes need adjusting

[gyroo]

Thanks Mad Muz,I"m glad things are quietening down on this thread now. I"m always on the hunt for RELIABLE information about gyro empty weights, rotor diameters, true engine hp, prop diameters, fuel capacity and thrust-line / CofG. The first 5 on this list come relatively easily from off the gyro register. The thrust-line / CofG is not so easily obtainable and has to be worked out carefully if any sort of reliable figure is to be obtained at all.By and large, our gyro community has come a fairly long way in the 3 decades since machines like the original Air Commands came on the scene. If one looks at the US NTSB fatality register by far the most common fatality machine is recorded as the Bensen B5, with the original Air Command coming in 2nd in the late 80"s and early to mid 1990"s. I"m not particularly concerned with the B5 accident rates, because a very large percentage of those involve completely unlicensed persons who had built a Bensen and then unwisely thought that they could fly it without lessons. Its with the original Air Commands that one can discern a trend toward PIO and PPO, and if one then crosses the Atlantic in the mid 90"s one sees that in the UK the original Air Command was grounded because of this.As a barrister I see that it is no co-incidence that the original Air Command business in the US and the original RAF business in Canada both failed under the weight of law suits against them arising from fatalities. And so it should have been in in an open marketplace. The designs ultimately killed just too many people and the businesses failed. That RAF has popped up again in South Africa is a great concern to me because the present day RAF coming out of South Africa is no improvement at all on the original, but the reason why it currently survives is that it is very, very difficult and hugely expensive for outsiders to sue South African corporations.Many ASRA members might have gained an impression that because I have frequently written about the thrust-line / CofG issue, that I am perhaps a I am obsessed with the issue. That is simply NOT the case. Thrust-line / CofG & HTL / CLT needs time and care to properly understandI do tend to write about it frequently because the implications of HTL are not easily understood or apparent, and even I will be the first to say that it is often not immediately apparent what the thrust-line / CofG of many machines are. I will also go so far as saying that from my experience, the thrust-line /CofG HTL issue appears to be actively misunderstood by some people, or even dismissed as nonsense by some blowhards. Because thrust-line / CofG is a characteristic that often can"t be intuitively worked out or worked out by guesswork, it needs to be ascertained by carefully done practical testing, or designed right from the outset by a careful arrangement of components of precisely known weight. ABOVE ALL, even if a gyro is high thrust line or even very high thrust-line, this fact alone won"t necessarily make it constantly dangerous, because PPO can really only come into play if the rotor is "unloaded" into reduced g below .5 g through to zero g. This might arise from clumsy maneuvering or PIO, or severe turbulence, or a combination of both. If a clumsily flown gyro has its rotor "unloaded" in severe turbulence, if it is centre-line-thrust (CLT) or near CLT, then it SIMPLY WON"T PPO. If it is HTL, depending on how HTL it is, and how fast its going, and whether there"s a working and effective horizontal stabiliser, then PPO is very much on the cards.The combination of HTL and reduced-g is the potential killerIf anyone is foolhardy, stupid or inexperienced enough to unload a gyro rotor to the point where its approaching zero-g (such as with a pushover nose-over at the top of a zoom climb that killed PeeWee Judge at Farnborough in 1967), if it is HTL it"ll probably flick into PPO. If it is CLT it won"t PPO. BUT - in either case if the rotor starts going into unconstrained flapping because the pilot is making panicky severe exaggerated "stirring the pot" control stick inputs that aren"t getting any response, then the tail feathers are in real danger of being struck anyway. In other words, because the reduced-g rotor isn"t capable of imparting any significant pitch or roll moment into the mast, the pilot unconsciously over-controls by putting in panicky ever-increasing large control stick inputs. This causes the reduced-g rotor to flap wildly to the point where it can be described as flailing (but it still won"t be capable of imparting any tilting or pitching moment to the mast). Remember also that when a rotor goes into reduced-g, autorotation also diminishes and the rotor will dramatically slow. The combination induced + parasite drag component from the rotor normally going into the mast and tending to hold the top of the mast back will also diminish in reduced-g, meaning that in that situation with a HTL gyro there is nothing holding the top of the mast back and the propeller thrust will then pitch and pivot the frame and mast forward around the lower-set CofG.A HTL machine will Power Push Over (PPO) under a reduced-g rotor by tumbling forward, whereas the CLT machine won"t pivot over into a tumble. The CLT machine might narrowly avoid destruction - the HTL machine won"t, because the gyro frame will be PPO tumbling under the flailing rotor. It only takes 10 to 20 degrees forward flick tumble into a flailing reduced-g rotor and IT"S ALL OVER. With a HTL gyro the landscape below will be littered with gyro and possibly body parts within seconds, whereas a CLT gyro might just survive the incident if the pilot puts g-loading back into the rotor in time. The sermon after this is therefore: DON"T UNLOAD THE ROTOR

[asra]

The only COG testing I have seen on a Euro gyro is on the late Michael Howards tandem Magni, at the nationals at Lamaroo .Tim McClure may have the original photo"s but from memory it was about 10 Inch HTL.

[birdy]

And flew like an arrow.Which would be good if riden arrows floats your boat.

[MadMuz]

This is a link to another Euro clone being produced now, which is basically a Ukrainian rip off off a magni crossed with a brako, crossed with a ela, crossed with a titanium

[MadMuz]

One thing I have noticed all through much of my reading of the thrustline situation, is that all of my machines have had the motor higher at the back so powering on loads the rotor but I never hear of this mentioned? Do people just run the motor (thrustline) parallel with the keel these days or do they still raise the back of the engine a few degrees?

[birdy]

It a way of fine tuneing your TL, but still an inefficiant bandaid if more than a couple degrees.

[gyroo]

Yeah - I completely agree with Professor Birdy. Altering the crankshaft axis angle of the engine is always on the cards for fine tuning. Most people seem to simply have the engine crankshaft axis parallel to the keel, but there are so many variables about whether the keel will be horizontal in flight it"s hard to recommend any guideline or design tip. If the keel is angled 3 or 4 degrees down in flight, then if the engine crankshaft axis is parallel to the keel, the propeller will have a downward thrust component of a few kilograms. If the keel axis is 3 of 4 degrees up in flight, then the propeller will have an upward thrust component of a few kilograms.

[MadMuz]

I just had the back of the engine (usually Subaru) with an extra washer height (2mm or so) in the rear mount than the front, it was about 5 degrees if that.... The Canberra guys (Quentin and the two Stans) said it was necessary.... never had any problem from it..... although it might not do much and it is not a "repair for bad handling or other issues) what it was explained to me is that it avoids a parabolic ark of the machine if one were to climb then level out and add power too soon.... if the rear of the engine happened to be lower (worn rubbers or just misaligned) than the front, then the prop would be pushing up (HTL) the rotors would be no longer climbing so a PPO could easily result. If the engine is tilted up at the rear.... even if the rubbers happened to sag, the engine could not sag so low as to be in the front high predicament.... so in other words, it is not done to fix anything, it is done so it can never reach the wrong angle. .... With the engine tilted high at the rear, if climbing and levelling out then adding power, the thrust actually positively loads the rotor, rather than making the frame unweight the rotor..... if you understand what I am getting at....

[gyroo]

Hi Mad Muz,It"s very good you raised this because it does highlight an important aspect of gyro dynamics. Changing the angle of an engine on a gyro frame can make a difference to the measurement of whether a thrust-line passes close to the gyro CofG or not. For a start, the thrust-line axis is (obviously) measured from the prop and is an imaginary line that goes forward. The CofG will be about 2 1/2 to 3 feet forward of the prop as an imaginary point somewhere normally lower down in the gyro frame.If the engine-prop combo is angled down at the front a little, the prop axis MUST run a little closer to the CofG than if the prop axis was parallel to the keel. If the engine-prop combo is angled relative to the keel a little down at the prop, then the prop axis MUST be a little higher away from the CofG than in the preceding sentence. The goal should be that the prop axis is closer rather than further away from the CofG, so lowering the front of the engine or raising the prop end of the engine is likely to do that. Sagging, soft or worn out rubber or polymer engine mount bushings make it likely that the prop axis will come a bit closer to the CofG at high throttle settings - I"m sure most of you have seen how far an engine moves on its mounts when doing a full throttle static thrust test - the front of the engine will be pushed hard down and forward a bit.So, the moral in this bit is that prop-axis-to-keel-angle MIGHT make quite a bit of difference to the thrust-line/CofG measurement. Front-of-engine-nose-down makes it much more likely that the thrustline measurement will be closer to the CofG, than if the engine is angled "prop down". As Birdy says, changing engine angle is only useful for tweaking - if a gyro is fundamentally a HTL gyro, then tweaking the prop axis angle a bit closer to the CofG is clearly a positive, but probably won"t improve the situation very much.The important bit The points made in the above paragraphs don"t really have too much to do with what the rotor is doing. Whether the keel is nose up or nose down is mostly immaterial to the rotor. Gyro pilots are "flying the rotor" at all times, and it doesn"t really matter too much whether the keel is angled nose down or angled nose to some extent. We"ve all seen the situation when a heavier person borrows a gyro and when it comes off the ground we have noticed that the keel is angled nose down quite a bit. As the gyro goes past viewers standing off to the side of the runway, viewers will notice that the heavy pilot has quite a bit of back stick already - that"s because he"s "flying the rotor", and not the keel. This is why hang testing is so vitally important, because in an extreme situation, a really heavy guy who borrowed a gyro and who then takes off with the keel really nose down will be holding a lot of back stick throughout the flight and may even not have enough back stick left to do a proper flare when landing.With helicopters as weight comes in and out of the cargo or passenger compartment at various stages of a flight, the fuselage "deck angle" changes with different loads and is quite noticeable, so a different stick position will be needed when the machine is picked up to a hover with varying loads. If you find the stick is 3/4 forward in the hover, then it"s not a good idea to continue because you"ll "run out of forward stick" as you approach cruising speed. If you find that you"re holding 3/4 back stick in the hover, then you need to think carefully because you might come close to "running out of back stick" in the chopper as you approach to land, and in an emergency a full autorotative flare might not be possible. So, remember - with all rotary winged machines the pilot is "flying the rotor", and gyro keel or helicopter fuselage deck angle is not particularly important UNTIL the stick range of travel is compromised in the ways described.But, hypothetically, if a gyro keel is either really noticeably nose down or nose up, then 2 issues do need to be considered: -(1) if the keel is really nose down, then a small percentage of the propeller thrust will be a downward-acting component, meaning the prop is pushing down a few kilograms and the rotor has to make up for that. (2) In a very noticeable keel nose-up situation, although the prop axis angled up might be adding a few kilograms up thrust, if the gyro has a good and effective horizontal stabilizer then clearly as the gyro increases in speed the tail will tend to pick up because the HS is like a small wing. This may or may not be a benign behaviour, and certainly the Sikorsky Blackhawk is a good example where the angle of incidence of the very large stabilator is computer controlled at all stages of flight to ensure the "deck angle" doesn"t get out of set parameters. Murray Barker reports that on his first-of-type flying of the Magni M24, he noticed that the pod went slightly nose down with throttle increases at lower speeds and that the pod nose came up slightly as speed increased as the big HS began to take effect (in effect pushing the tail down a bit). To what extent the M24 maximum rate of climb is compromised by the HS pushing the tail down a bit is unknown - it wouldn"t be much, I would think. Mark Regan

[MadMuz]

Thanks Mark, I am not thinking of the engine tilt as any form of cheating, nor masking of thrustline issues, purely as a machines response to throttle, not including the obvious nose movement on thrust increase in a HTL machine.... but what was explained to me back in the day and the reason I tilt the engine is this:If you are flying along on a calm day straight and level in a fairly powerful gyro, just an example, say 5"HTL.... you have your motor level with the keel.... you apply liberal power, the machine pushes forward with a little nose down and increases speed or begins to climb a little..... in the same machine, same scenario, with the engine perhaps sagging down at the rear (perhaps tired rubber mounts) as you apply power, the resulting thrust would push the motor up towards where the thrust line is pointing, which would actually unweight the rotors a little, which is not good....

[Adrian S]

Mark, Tim, Birdy, Murray and Mad Muzz,Compliments on the quality of your responses. This is info that we should published regularly in the ASRA magazine. It makes my job as a ASRA TA easier when I knock someone back for presenting a "std RAF 2000" or explain that most Euro designs are HTL that is managed by a large Horizontal Stab. Thanks,Adrian S